Add to Cart Buy Now Buttons

Both those page have working add-to-cart buttons for me, so maybe you are seeing cached pages.

Your theme is version 1.1.4 but 1.3.0 has WP 4.4 support, see the changelog:
https://themeforest.net/item/wemusic-music-band-event-wordpress-theme/12251286
If updating, take a backup.

Hello, thank you for the response, I just checked it in Chrome and Safari and I’m seeing the button, but not Firefox.

I have re-tested, my experience was:
Chrome: works properly, able to add multiple items
Safari: no button
Firefox: button appeared, allowed one add-to-cart, then no button
IE: button appeared, allowed one add-to-cart, then no button

I still think the theme update is the next step to try.